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ERESE > Activities > Introduction to the structure of the ocean using CTD data

Introduction to the structure of the ocean using CTD data

Shawn Doan, Sehome High School Bellingham, WA
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This material is replicated on a number of sites as part of the SERC Pedagogic Service Project

Summary

Students use real CTD (Conductivity, Temperature, Depth) data and their own experiences to learn the basic structure of oceans. Depth, light, temperature, oxygen, salinity and pressure are considered. Students should have some graphing experience and some familiarity with the concept of dissolved oxygen in water.

Grade Level: 9 -12
Duration of Lesson: 4 hours class time

Learning Goals

Students will learn the distribution of light, temperature, oxygen, pressure and salinity with depth in the ocean. They will practice their reasoning, communication and graphing skills. They will learn how their own experiences can help them interpret scientific data. They will graph real data and explain its meaning.

Context for Use

This unit was designed for 9-12th grade students in an environmental science or oceanography course. The average student should have some basic graphing skills, and be familiar with concepts such as photosynthesis, respiration. Students will also find it helpful to know that cold water has a great capacity for dissolved oxygen than warm water. My students have all worked with photosynthesis, respiration and dissolved oxygen prior to this unit.

It makes sense to follow this unit with one on themohaline circulation because this unit introduces concepts needed to understand thermohaline circulation. Students can then compare CTD data from source water areas to confirm some aspects of the thermohaline model.

Description and Teaching Materials

Structure of the ocean and properties of seawater with regard to: light, temperature, dissolved oxygen, pressure and salinity


Summary


for details see:

Two Layer Ocean Lesson Plan
Detailed lesson instructions to students with notes to teachers.

Two Layer Ocean Pretest
Pre- and Post-test for use with this lesson.

Two Layer Ocean Pretest Key
Pre- and Post-test with answers highlighted.

1. Students use journals to respond to thought problems concerning light and temperature in shallow and deep water. Questions will be interspersed with discussion about student ideas and observations.

2. Students graph their preconceptions and consider the relationship between light and water temperature. Students learn to graph with multiple axes.

3. Students graph CTD data collected October 2007 near Hawaii. This data includes depth, pressure, temperature, salinity and dissolved oxygen. Students compare graphs.

The following images can be used to introduce the CTD data set:
Pictures of CTD Deployment

CTD Deployment Diagram

The following files are used during student graphing:
Tropical Pacific CTD Data 50m intervals
This Excel file contains data to be graphed by students. Extra columns for elapsed time, bottles fired and sound velocity are not required.

Tropical Pacific CTD Data 1m intervals - BIG Table!
Excel file containing more, but not all, of the data collected during this CTD deployment. It is used to give students a better idea of how much data is collected.

Example Tropical Pacific CTD Profiles
Example graph made using similar data.

4. Students respond to questions about depth, pressure, temperature, salinity and dissolved oxygen and consider the causes of their variations with depth in the tropical Pacific.

Temperature Latitude Diagram This picture can be used in discussion to show source areas for cold bottom water.

5. Discussion leads students to the concept of a two layer ocean model (dominated by a warm light layer and a cold dark layer). The two layer ocean emphasizes the lack of primary productivity below the photic zone and the dominance of respiration in the deep sea. Students can then use the data and their graphs to discuss how the two layer model is supported or not supported by the data.

This lesson is followed by a lesson on thermohaline circulation.

Note: This lesson can be shortened by removing some of the thought problems or by printing the questions for the students.

Two Layer Ocean Lesson Plan
Detailed lesson instructions to students with notes to teachers.

Two Layer Ocean Pretest
Pre- and Post-test for use with this lesson.

Two Layer Ocean Pretest Key
Pre- and Post-test with answers highlighted.

Pictures of CTD Deployment
Pictures of CTD deployments aboard the Kilo Moana, Oct, 2007.

CTD Deployment Diagram
Diagram showing principles of CTD deployment.

Tropical Pacific CTD Data 50m intervals
This Excel file contains data to be graphed by students. Extra columns for elapsed time, bottles fired and sound velocity are not required.

Tropical Pacific CTD Data 1m intervals - BIG Table!
Excel file containing more, but not all, of the data collected during this CTD deployment. It is used to give students a better idea of how much data is collected.

Example Tropical Pacific CTD Profiles
Example graph made using similar data.

Temperature Latitude Diagram This picture can be used in discussion to show source areas for cold bottom water.

Teaching Notes and Tips

The unit can be broken into 3 or 4 one hour segments depending on the skill level, motivation and discussion time allotted. Students should do their own work in journals or notebooks that will be assessed at the end of the unit. Pairs of students can work together to graph the CTD data set.

The first two days of questions and answers are trying for some students. Breaking this up with pictures of research work or deep ocean creatures gives students a breather and helps keep them engaged.

Prep: Make overheads of questions for students to respond to. Make copies of the Tropical Pacific CTD Data 50m intervals data table so that there is at least one copy for every two students.
It is helpful to collect pictures of ocean sampling, swimming in lakes, and light changes in deep water to prompt discussion.

Assessment

Assessment of Students: Students are assessed by the completeness of their journal entries, the accuracy of their CTD graphs, and their score on the post test. While journal entries don't have to be "correct", they should show that directions were followed and that answers are thorough.
Lesson Evaluation: The effectiveness of the lesson can be evaluated by comparing the pre- and post-test scores.

References and Resources

http://earthguide.ucsd.edu/earthguide/diagrams/woce/
Repeated CTD deployments can be used to characterize the ocean 3 dimensionally. This link shows how seawater parameters change with latitude. They are North-South cross sections of the ocean basins. Courtesy of WOCE and National Oceanographic Data Center.

http://earthguide.ucsd.edu/earthguide/diagrams/levitus/
Repeated CTD deployments can be used to characterize the ocean 3 dimensionally. This link shows how seawater parameters change with depth in the ocean. Stepping through this animation allows you to peel off subsequent layers of the ocean exposing the continental shelves and mid-ocean ridges. Courtesy of Lamont-Doherty Earth Observatory

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